Cardiac pacemakers, and other cardiac stimulation devices, such as defibrillators, are now routinely used by physicians around the world. These devices are surgically implanted within a patient and have electrical leads that conduct signals to the patient's heart. Advances in the electrical and electronic technologies have been applied to pacemaker devices to improve the performance, reliability, and programmability of such pacemakers. Many of these advances are exploited by using a communication link established between an implanted pacemaker and a device called a "programmer". For example, pacemakers in use today have the ability to communicate with a programmer via an RF link. The programmer can receive data from the pacemaker as well as transmit both data and programming instructions to the pacemaker. A communication channel is established between a pacemaker and a programmer by placing a telemetry head, which is connected to the programmer, over the implant site (e.g., chest or abdomen) of a patient. The telemetry head functions as an antenna for transmitting and receiving RF signals.
Once an operational telemetry link is established between a pacemaker device and a programmer unit, data transfer between the two devices can occur. During this data-transfer period, information representing the patient's past heart activity is typically downloaded from the pacemaker to the programmer. Additionally, the pacemaker will typically transmit real-time data representing the patient's present cardiac activity. In some cases, the communication link is used to program and reprogram the pacemaker.
During the real-time data transmission, the telemetry link between the pacemaker and the programmer can be disrupted. Disruption of the telemetry link can result from relative movement between the patient (i.e., pacemaker), and the telemetry head. Disruption of the communication channel can also result from excessive noise picked up by the telemetry head, or when the telemetry head and the pacemaker become separated by too great a distance. If any of these conditions occur, the communication link may be broken and all data transmission will correspondingly cease. Typically, the attending medical personnel first realize a problem exists with the communication link when he or she attempts to communicate with the device. Once broken, it is necessary for the physician to reestablish the communication link to continue the monitoring and/or programming procedure. This process is time-consuming and delays the intended operation.
Aside from being time consuming, problems with obtaining and maintaining an adequate RF communication link can lead to catastrophic results. For example, an attending physician who experiences difficulty in establishing or maintaining a communication link with an implanted pacemaker may take improper action if the physician does not know the precise reason for the difficulty. Specifically, without information as to the status and quality of the communication link, the physician may conclude that the pacemaker is defective. In such a situation, the physician could erroneously recommend replacement of the pacemaker when, in fact, the problem could have been corrected without invasive surgery by establishing a proper communication link.
Advances in pacemaker technology have resulted in various improvements in the way data is transmitted between the pacemaker and the programmer. Other improvements relate to methods of processing the data. For example, in U.S. Pat. No. 4,596,255 issued to Snell et al., there is disclosed an apparatus connected to an implanted pacemaker which interprets and displays a patient's cardiac events. The apparatus disclosed in Snell simultaneously receives information from the pacemaker and information from ECG electrodes placed on the patient. The information from the pacemaker is synchronized with the information from the ECG and subsequently displayed in real-time on a video screen. This allows an attending physician to quickly evaluate the functioning of both the pacemaker and the patient's heart.
Disclosed in U.S. Pat. No. 4,791,936, also issued to Snell et al., is a separate apparatus for interpreting and displaying a patient's cardiac activity in conjunction with the signals generated by a cardiac pacemaker. The apparatus disclosed utilizes multiple interpreters to process information received from a telemetry head, which in turn receives the information from the pacemaker via an RF communication link. According to the '936 patent, the information received represents different cardiac events, such as atrial or ventricular contractions. This information, along with ECG information received from a separate interpreter, is synchronized. The resulting synchronized information is then processed before being displayed on a video screen in real-time.
Other patents which disclose apparatus and methods for communicating with, monitoring, and/or programming the actions of a pacemaker include U.S. Pat. No. 4,809,697 issued to Causey, III et al., and U.S. Pat. No. 5,309,919 issued to Snell et al.
All of the above-described patented devices use noninvasive telemetry to configure the specific operation of the pacemaker in accordance with the needs of an individual patient. Noninvasive telemetry is accomplished through the use of an RF communication channel. While various ways have been developed to improve the type and amount of data received through this communication channel and the format of displaying the data, little attention has been directed to the monitoring of the quality of the communication channel.
When monitoring and/or programming cardiac pacemakers, the quality of communication is important because many problems associated with telemetry occur if the telemetry link, i.e., the communication channel, is never properly established. In some problematic cases, the telemetry link may at first be properly established but for any of a number of possible reasons, the link is subsequently broken. Thus, there is a need in the art for a telemetry system which can monitor the status and quality of the communication channel to correct deficiencies in channel quality during the procedure of communicating with, and programming a cardiac stimulation device.